1. Field of the Invention
The present invention relates to a cross-linked polymer solid electrolyte.
2. Description of the Art
Conventional polymer solid electrolytes based on polyethylene oxide (PEO) or on polypropylene oxide (PPO) have low ionic conductivity at ambient temperature (10.sup.-7 S/cm). Only the amorphous phase provides conduction, and conduction is only really good beyond the melting temperature of the polymer. By reducing the vitreous transition temperature of the polymer, eliminating crystalline zones and using smaller molecular masses, it is possible to increase ionic conductivity. The counterpart of these improvements is often a considerable degradation of mechanical properties.
Film strength can be increased by cross-linking conductive polymers, but this reduces conductivity.
Polymer solid electrolytes are also known that include plasticizing agents.
In the article by P. M. Blonsky and D. F. Shriver published at pages 6854-55 of J. Am. Chem. Soc. 1984.106, a polymer of the poly(bis(methoxy ethoxy)phosphazene) type is described which incorporates short chains of PEO whose ionic conductivity at 25.degree. C. exceeds 10.sup.-5 S/cm. Both the electrochemical stability and the mechanical properties of this new compound are limited.
In patent document U.S. Pat. No. 4,654,279, Bauer et al. describes a polymer solid electrolyte constituted by two interpenetrating phases: a cross-linked inert solid phase and a polymer liquid phase (a low mass polyether) having good ionic conductivity (&gt;10.sup.-4 S/cm). The relative proportions of the cross-linked phase and of the liquid are chosen so as to combine good mechanical properties and good electrochemical properties. The ionic conductivity of this electrolyte is of the order of 10.sup.-4 S/cm at ambient temperature.
In patent document U.S. Pat. No. 4,792,504, G. Schwab and M. T. Lee disclose a solid electrolyte whose matrix supporting the liquid phase is constituted by PEO cross-linked by a compound of the polyacrylate type. The liquid in which a metal salt is dissolved in a low molecular mass polyether or an aprotic solvent.
Patent document EP-A-037 776 describes a cross-linked polymer solid electrolyte including a polyether having amine functions cross-linked by a curing compound that may include two epoxy functions. This electrolyte can only be used satisfactorily, i.e. with adequate ionic conductivity, at a high temperature of the order of 70.degree. C. to 100.degree. C.